Pāṇini sūtras

A long vowel is substituted for the a of the reduplicate in the Intensive (with expressed or elided yaṅ), when the reduplicate receives no augment having an indicatory k

1. dīrghaḥदीर्घः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   dद्	dīrghaदीर्घ	dīrghaḥदीर्घः	long	dīrghदीर्घ् + plus aḥअः

2. a+k+itaḥअ+क्+इतः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	aअ	aअ	not	aअ
   kक्	kक्	kक्	kakāraककार	kक्
   iइ	itइत्	itaḥइतः	itइत्	itइत् + plus aḥअः

Anuvṛtti

1. abhyāsasyaअभ्यासस्य 7·4·58

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	abhyāsaअभ्यास	abhyāsasyaअभ्यासस्य	reduplication	abhyāsअभ्यास् + plus asyaअस्य

2. yaṅ+lukoḥयङ्+लुकोः 7·4·82

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   yय्	yaṅयङ्	yaṅयङ्	intensive ending	yaṅयङ्
   lल्	lukलुक्	lukoḥलुकोः	suffix elision	lukलुक् + plus oḥओः